Now that a new comic is posted, everyone who doesn't want to hear the logic debate will have likely moved on anyway. So let me post a scenario to those who still think arguments from authority are always fallacious.

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You've been given the job of preparing for a major event, let's say a county fair. The scene is your office. It's the evening before the fair, and you're working late on last-minute paperwork.

A man walks in. He shows you an FBI badge (or whatever the equivalent is in your own country).

Man: "We think someone has hidden a bomb on the fairgrounds. They plan to detonate it tomorrow during the fair, when the crowds are at their thickest."

You: "How do you know?"

Man: "I can't tell you that. It would endanger my source."

You: "What do you want from me?"

Man: "Cancel the fair. I don't have the authority to do it myself, and I don't have time to search the entire grounds before tomorrow."

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Is it fallacious to act on the man's warning?

It depends on the logic you use to justify it. It is not inherently fallacious in and of itself.
His authority in of itself doesn't definitely prove that his claim is correct. It just tells us that he lays claim to authority and is making a proposition about reality.

We can't know if he's lying or if his badge is real. We can't know if he's simply wrong. FBI agents aren't inherently incorruptible or correct. As plenty have been attempting to entrap suspected terrorists based on profiling and moles. There's plenty of those types who think the ends justify the means.

Without any further information, just having authority is unsatisfactory.

Authority doesn't definitely provide proof positive. (And while doesn't disprove him either. All that tells us is that we don't know.) It is just a sort of power imparted by status. We may be compelled to act on the basis of his power, but that doesn't speak to the truth of what he is saying.

It would be better if he can at least establish some lines of evidence because that holds him accountable to a small degree. (Not an infallible degree, but far preferable to authoritarianism.) And a professional reputation that we know about is also useful for similar reasons.

Again, you're confusing matters of pure logic with matters of politics, psychology and other social dynamic stuff.

If the Bush administration claims that Saddam has WMD's and ties to Bin Laden, then he can get his way with invading Iraq, either by the gullibility of his constituency or because of the power invested in him by the political system, by organization inertia or whatever. The facts outed themselves later, but nobody held him accountable.

Synar wrote:

I think the problem here is one third of us are discussing pure logic, or how one can rigorously draw a conclusion from predetermined predicates,
one third of us are discussing rhetorics, or how one can convince somebody of the truth of his point,
and one third of us are discussing epistemology, or the science of understanding how one can know things.

Appeal to authority should be fine to use in the second case, and admittedly in the third. It is a fallacy when discussing pure logic. Now that the confusion is cleared hopefully everyone can start discussing erfworld again.

I'd fight you on the point of epistemology. Belief is not a committed all-or-nothing. Taking a gambit based on likely outcome is not at all the same as complete and total faith in a proposition. You act on assumptions because you must and correct your course as new evidence gives you reason to revise your models.

This is the trouble. People think knowledge is some absolutist thing. What it really is that you are making a claim that your belief is true and informative within certain acceptable tolerances.

So you're so sure the bomb doesn't exist that you're willing to stake hundreds of lives on it? Even though the FBI man could have very good reasons for not telling you his evidence? (Remember, he says doing so would endanger his source.)

Fine, whatever, here's an even more obvious example:

You're taking care of your elderly grandmother, who has dementia. While you're in the next room, she finds some antifreeze, mistakes it for something edible, and drinks it.

You don't realize what happened until she vomits. You call 911 (or your local equivalent), who redirects you to poison control.

Poison Control Lady: I'm sending an ambulance. In the meantime, do you have any spirits?
You: What? You mean alcohol? I think there's some brandy.
Poison Control Lady: Give it to her.
You: Why?
Grandma: *hyperventilating*
Poison Control Lady: Because it'll help her last until the ambulance arrives.
You: Yeah, but how do you know that?
Poison Control Lady: Because that's what they taught me in job orientation! Hurry up!
You: But that's still just an argument from authority.
Grandma: *writhes in pain*
Poison Control Lady: What do you expect!? I'm only paid $10 an hour! Just help her already!

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Poison Control Lady doesn't know why alcohol will keep her alive. Do you do still do what she asks?

Let me put it this way. The way you presented that FBI officer is fucking shady as hell. It's indistinguishable from a bomb threat. He won't prove his credibility in any way shape or form and wants you to shut down on pretty much no rationale at all. That sounds like a way to obstruct the fair or cost somebody a lot of money, if not an outright attempt at terrorizing or trolling people.

You are also appealing to my emotion of fear. Which has nothing to do with reason. I resent it immensely as an attempt at manipulation. And I resent the "what if you're wrong" games that people like to play. Yes, if I'm wrong, maybe there really is a ten-armed monster with sharp teeth around that very corner over there. But this is essentially speculation and doesn't actually inform our behavior.

You are talking about risk assessment to be sure. But as I stated, taking gambits has little or nothing to do with whether something constitutes positive proof in full. Appeal to authority does not qualify. It doesn't not establish a chain of reasoning from premise to conclusion that is logically valid.

I'm not trying to manipulate your emotions, I'm doing, as you mentioned, risk assessment. And considering if you're wrong is not "a game people like to play". It's critical to arriving at the truth, because no one's right about everything. If I never questioned my own conclusions, I'd never correct myself and grow.

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But as I stated, taking gambits has little or nothing to do with whether something constitutes positive proof in full. Appeal to authority does not qualify. It doesn't not establish a chain of reasoning from premise to conclusion that is logically valid.

It depends on what your conclusion is. If your argument is "This scientist says X, X must be true", then that's definitely faulty logic. If your argument is "This scientist says X, X is more likely to be true than I previously thought", that's an entirely valid conclusion. And when 99.999% of scientists say the Earth revolves around the Sun, it's logical to believe that they're probably right.